Coal bin



FIG. 1 is a perspective view of a coal bin showing my new design;

FIG. 2 is a front plan view thereof;

FIG. 3 is a rear plan view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a side plan view thereof;

FIG. 6 is a bottom plan view thereof.

The ornamental design for a coal bin, as shown and described. 